Water curtains

Water curtains can also cool or eliminate available ignition source to a released vapor cloud. In this fashion they can also be a mitigating feature to prevent vapor cloud explosions. Hot surfaces, sparking devices and open flames in the immediate area of a vapor release can all be eliminated as a result of a directed water curtain where these sources exist. 

For water curtains to be highly effective they should be automatically activated upon confirmed gas detection for the area of concern. 

A patented water injection system has been devised for extinguishing oil and gas well fires in case of a blowout. The Blowout Suppression System (BOSS) consist of finely atomized water injected to the fluid stream of a gas and oil mixture before it exits a release point. The added water lowers the flame temperature and flame velocities thereby reducing the flame stability. In the case where the flame cannot be completely dissipated, the fire intensity is noticeably deceased, preserving structural integrity and allowing manual intervention activities. A precaution in the use of such a device is that, if a gas release fire is suppressed but the flow is not immediately isolated, a gas cloud may develop and exploded that would be more destructive that the pre-existing fire condition. 

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The next step is to apply a number of loss control credit factors such as process control (emergency power, cooling, explosion control, emergency shutdown, computer control, inert gas, operating procedures, reactive chemical reviews), material isolation (remote control valves, blowdown, drainage, interlocks) and fire protection (leak detection, buried tanks, fire water supply, sprinkler systems, water curtains, foam, cable protection). The credit factors are combined and appHed to the fire and explosion index value to result in a net index. 

Countermeasures Water sprays Water curtains Steam curtains Air curtains Deliberate ignition of explosive cloud Dilution Foams... 

Pollution tree paint fumes through water curtain... 

A spray booth can be installed as discussed above and provided with a running-water curtain system and an exhaust arrangement to absorb the oversprayed paint and its fumes. The paint fumes are circulated through the curtain of water and the harmless fumes are then discharged to the atmosphere. 

The wash water mixed with paint which is a strong waste can be transferred (periodically, if the water curtain system is a closed cycle rather than a continuous running water system) to the effluent treatment plant for further treatment, as shown in Figure A13.12. 

A similar logic is applicable to the control of explosions involving gas or vapour, but other measures, e.g. dispersion by steam or containment by water curtains, may be applicable to vapour clouds in the open air. Containment or diversion of a blast (e.g. by blast walls) and reducing its effect by appropriate spacing of equipment, buildings etc. are also applicable. 

Water rinses are used in surface preparation operations such as acid pickling, alkaline cleaning, and nickel deposition to remove any process solution film left from the previous bath. A water rinse may also follow the neutralization step. Another common water use is in the ball milling process, which uses water as the vehicle for the enamel ingredients, as a cooling medium, and for cleaning the equipment. Coating application processes normally use wet spray booths to capture oversprayed enamel particles. Water wash spray booths use a water curtain into which the enamel particles are blown and captured. 

These proposed passive safety systems minimize the need for active safety installations in storage, such as the provision of water cooling or water curtains. 

Water is not suitable for electrical (Class C) fires, but is effective on all combustible (Class A) and many flammable liquid (Class B) fires. Water can be applied by hose streams, monitors, sprinklers, water spray systems, or as water curtains for such purposes as ... 

The EDV Wet Scrubbing System utilized proprietary nozzles to produce high-density water curtains through which the gas must pass. Each nozzle sprays water droplets that move in a cross-flow pattern relative to the flue gas. These cover the entire gas stream and uniformly flush the vessel s surfaces clean. The spray nozzles are nonclogging and are designed to handle highly concentrated slurries. 

SO2 absorption and particulate removal begins at the quench section and continues as the flue gas rises up through the main spray tower where the gas is again contacted with high-density water curtains produced by additional spray nozzles. The spray tower itself is an open tower with multiple levels of the BELCO spray... 

Little data are available to estimate releases of isophorone to water. During isophorone manufacture, process water may contact the isophorone and carry some of it to wastewater streams. During use of isophorone, paint spray booths that use water curtains, wash water, and process water all may contain isophorone. Isophorone has been detected in the United States in industrial effluent... 

The most common method for cleaning the gun is to put a small amount of solvent into the pressure pot or cup gun, and clean the gun by spraying directly into the water curtain or dry filter of the spray booth. This is an unnecessary and expensive generation of waste. Both air emissions and waste paint are generated. In some states, notably California, regulations require that the paint operator spray gun cleaning solvents into a closed container so as to minimize VOC solvent emissions. This practice also allows recycling of the paint sprayed into the container (Joseph 1989). 

Napier, D.H., Generation of Static Electricity in Steam Screens and Water Curtains, Paper P, Institution of Chemical Engineers Symposium Series No. 39, London, 1974. 

Eggleston, Herrera, and Pish 1976 To provide needed data about the use of air entrained by a water spray to dilute flammable vapor releases below the lower flammability limit. Absorption/adsorption effects are insignificant in the case of ethylene and vinyl chloride. Sprinklers and water-spray nozzles vary widely in their efficiency as air movers. Flame quenching was not affected in any of the experiments Water sprays increased the rate of flame propagation. The air-pumping action of a water curtain can be used to set up a barrier to the horizontal flow of vapors. 

Emblem and Madsen 1986 To check the efficiency of a full-scale water curtain installation by simulating an actual gas release using CO2 as the test gas. The main effect of the water curtain was to dilute the maximum concentration region and form a cloud of almost homogeneous concentration. In this case the nozzle spacing was so wide that the effect of the barrier was small. 

Blewitt, Yohn, Koopman, Brown, and Hague 1987 Test the effectiveness of water sprays to mitigate HF releases. Water curtain spray systems achieved approximately a 36 to 49 percent reduction in downwind concentrations of HF. This reduction is consistent with labortory experimental data. The compressed air and water spray appeared to be less effective than the water-spray curtain. 

The time required for actuation is a critical issue. Cloud travel time to sensitive areas can be achieved in a few seconds for jet releases and in a few minutes for refrigerated releases. Therefore, to be effective, water curtains must be designed to be activated within a short time of the onset of a release. 

Water curtains can be an effective postmitigation technique. Their optimal design is best addressed on a case-by-case basis. 

When nozzles are used in water curtains it is necessary to ensure that the spray pattern produced will be resistant to the prevailing meteorological conditions. 

The size of the droplets produced by a spray nozzle is an essential piece of information as shown in the earlier discussions of water curtains. The droplets must provide adequate surface area for absorption to mitigate a vapor cloud of material having good water solubility. When a water curtain is to be used to mitigate a vapor cloud by diluting it, then the volume of the droplets (i.e., its momentum) is important. 

In cold climates, especially when temperatures are below freezing, a water curtain may suffer operating problems when ice forms at the spray nozzles or the water drops produce snow. Either of these occurrences could result in a significant reduction in the effectiveness of a water curtain. 

Emblem, K. and O. K. Madsen, 1986. Full Scale Test of a Water Curtain in Operation. 

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